Spectra Statistics for the Odd-Odd Nucleus ⁸⁶Nb

The energy levels of the odd-odd nucleus ⁸⁶Nb at low spins are calculated by using quasi-particles plus a rotor model. The distribution of the nearest-neighbor spacing and the spectral rigidity are studied. We find that the chaotic degree of the energy spectra increases with the increasing spin and reaches a maximum at I = 10; then it decreases gradually for the spins above I = 10. The recoil term in the model Hamiltonian makes the energy spectra slightly regular. The Coriolis force, however, makes the spectra chaotic and plays a major role in the spectral statistics of the odd-odd nucleus ⁸⁶Nb.